[Paddlewise] okoume plywood

I am about to built my forth kayak and I've just begun to see that there 
might be grades of okoume plywood (I'm a slow learner). The prices in and 
around Rhode Island range from $39 to $88. a sheet for 3 mm. The highest 
price lumber yard claims theirs is top grade marine. Does anyone know more 
about this so I can compare apples to apples?  The last plywood I got (two 
years ago) was definitely of an lesser quality than years before but it 
didn't occur to me that there might be either different grades or different 
manufacturers. 
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